1. Field of the Invention
The present invention relates to a gear finishing apparatus for honing a gear blank having gear teeth to finish the gear teeth.
2. Description of the Prior Art
Automotive transmissions and differentials, for example, have a number of gears that are required to be finished highly accurately, i.e., to very close dimensional tolerance. Such gears are manufactured by cutting gear teeth in a gear blank with a hobbing machine, for example, finishing the gear teeth with a gear shaving machine or the like, and then honing the gear teeth to a highly accurate finish that is desired.
One known honing apparatus is disclosed in Japanese laid-open patent publication No. 2-284819 or No. 3-202225, for example. As shown in FIG. 13 of the accompanying drawings, the disclosed honing apparatus has a workpiece support shaft whose axis P extends horizontally, with a gear blank W being rotatably supported on the workpiece support shaft, and a grinding wheel 51 in the form of an internal gear having gear teeth complementary in shape to the gear teeth and held in mesh with the gear blank W to be finished for finishing the gear teeth of the gear blank W. In order to finish the gear teeth of the gear blank W, the grinding wheel 51 is rotated with its rotational plane being tilted at an angle .theta. to the vertical plane.
The grinding wheel 51 is employed because the internal gear configuration thereof achieves a high contact interval for better finishing efficiency. The axis of the grinding wheel 51 is tilted at the angle .theta. to the vertical plane in order to give slippage along the gear teeth for a higher honing effect.
However, since the axis P of the workpiece support shaft which supports the gear blank W extends horizontally, and the grinding wheel 51 is tilted at the angle .theta. to the vertical plane, it is necessary to provide increased bearing rigidity for bearing the reactive forces that are produced when the gear blank W is machined, and such increased bearing rigidity results in an increase in the size of the honing apparatus.
More specifically, as shown in FIG. 13, in order to tilt the grinding wheel 51 at the angle .theta. to the vertical plane, the grinding wheel 51 is required to be angularly displaced about a horizontal axis that passes through the center O of the gear blank W perpendicularly to the sheet of FIG. 13, and the grinding wheel 51 and the gear blank W are required to mesh with each other at a meshing point that is as high as the center O. The distance h from a base 52 of the honing apparatus to the axis P of the workpiece support shaft has to be equal to at least the radius of the grinding wheel 51. Because of this large distance P, the bearing rigidity for bearing the reactive forces produced when the gear blank W is machined must be of a large setting, and the vertical dimension of the honing apparatus must be relatively large. The horizontally extending workpiece support shaft results in an increase in the width of the honing apparatus.
Other problems with the conventional honing apparatus are that it is very cumbersome to install the gear blank W on and remove the gear blank W from the workpiece support shaft, and chips produced when the gear blank W is cut fall onto the base 52, which tend to be deformed or damaged due to the heat carried by the chips and stored in the base 52. Any deformation or damage of the base 52 is detrimental to the accuracy, such as dimensional accuracy, of the finished gear.